A process for the preparation of a halogenated metal phthalocyanine catalyst suitable for sweetening of sour petroleum distillates.
Particularly the invention relates to a process for the preparation of various halogen containing derivatives of different metal phthalocyanines, useful for sweetening (oxidation of thiols to disulphides) of petroleum fractions like FCC gasoline, jet fuel, kerosene, heavy naphtha, thermal gasoline, diesel and distillate fuel oil.
It is well known that the presence of mercaptans in the petroleum products like LPG, naphtha, gasoline, kerosene, ATF etc. is highly undesirable due to their foul odour and highly corrosive nature. These are also poison for the catalysts and adversely affect the response of TEL (tetraethyl lead) as octane booster. Although there are several processes known for the removal of mercaptans from these petroleum products, the most common practice is to oxidize the mercaptans present to less deleterious disulphides with air in the presence of a catalyst. Commonly lower mercaptans present in LPG, pentanes, LSRN are first extracted in alkali solution and then oxidized with air in the presence of a catalyst. The higher molecular weight mercaptans present in petroleum products like FCC gasoline, LSRN, thermal gasoline and distillate fuel oil are oxidized to disulphides with air in presence of alkali in a fixed bed reactor containing catalyst impregnated on a suitable support (Catal Rev. Sci. Eng. 35(4),571-609(1993).
In the hitherto known processes, phthalocyanines containing metals like cobalt, iron and manganese are used to catalyze the oxidation of mercaptans to disulphides in alkaline medium. Among these cobalt and vanadium (especially cobalt) phthalocyanine and their derivatives are preferred. As these metal phthalocyanines are not soluble in aqueous medium, for improved catalyst activity their derivatives like sulphonated and carboxylated metal phthalocyanines are used as catalysts for sweetening of petroleum fractions. Various catalysts reported are cobalt phthalocyanine monosulphonate (U.S. Pat. Nos. 3,371,031; 4,009,120; 4,207,173; 4,028,269; 4,087,378; 4,141,819; 4,121,998; 4,124,494; 4,124,531), cobalt phthalocyanine disulphonate (U.S. Pat. No. 4,250,022), tetrasulphonate (U.S. Pat. No. 2,622,763), mixture of mono- and disulphonate (U.S. Pat. No. 4,248,694), phenoxy-substituted cobalt phthalocynine (Ger. Offen 3,816,952), cobalt and vanadium chelates of 2,9,16,23-tetrakis (3,4-dicarboxybenzoyl) phthalocyanine for both homogeneous and fixed bed mercaptan oxidation (Ger. Offen 2,757,476: Fr. Demande 2,375,201) and cobalt and vanadium chelates of tetrapyridinoporphyrazine (Ger. Offen 2,441,648).
It is also hitherto known that because of poor solubility of cobalt phthalocyanine in aqueous or other medium it is difficult to impregnate the same on the bed of catalyst support material. The highly sulphonated or other similar derivatives of cobalt phthalocyanine, though are soluble in the impregnating solution, their high solubility makes it difficult to place the required amount of catalyst on the support material. Furthermore, the more highly sulphonated or other similar substituted metal phthalocyanines are susceptible to leaching from the catalyst support when it is made alkaline with sodium or potassium hydroxide solution. The leaching causes loss of catalyst from the bed.
Metal phthalocyanine monosulphonate are thus the preferred compounds for impregnation on the support material in the fixed bed sweetening. The most common method used for their preparation is the reaction of metal phthalocyanine with oleum or sulphuric acid. However this reaction is difficult to control so as to produce metal phthalocyanine monosulfonate, exclusively because in this reaction, along with monosulphonate di- and tri-sulphonated derivatives are also formed. These derivatives of metal phthalocyanines, especially of cobalt phthalocyanine are much more soluble in hydrocarbon and in caustic solution than the former. This solubility characteristic is very important when the catalyst is used for the fixed bed sweetening of petroleum fractions. The catalyst once placed on the carrier must remain attached so that catalytic activity is maintained. The catalyst therefore should be such that it could be easily impregnated on the fixed bed material and yet is not leached out by alkali solution or hydrocarbons during the sweetening process.
Use of oleum during the preparation of metal phthalocyanine monosulphonate also posses waste disposal problems. Isolation of metal phthalocyanine monosulphonate from the reaction mass also affects the economics of the process.
The main objective of the present invention is to develop a process for the preparation of novel metal phthalocyanine based catalysts useful for sweetening of petroleum fractions like kerosene, FCC gasoline, jet fuel, heavy naphtha, thermal gasoline, diesel and distillate fuel oil in a fixed bed by impregnating the catalyst on a suitable support, which obviates the drawbacks as detailed above.
Accordingly the present invention provides a process for the preparation of a supported catalyst comprising a Halogenated Phthalocyanine of cobalt, iron or manganese of formula 1
which comprises: mixing a phthalocyanine of cobalt, iron or manganese with a halogenating agent in a stoichiometric ratio ranging between 1:1 to 1:20 optionally in an inert organic solvent, refluxing or heating and stirring for a time period ranging between 1-6 hrs, distilling the excess halogenating agent from the mixture, filtering and washing the residual mass by known method to obtain the desired halogenated phthalocyanine and impregnating a support material with the desired halogenated phthalocyanine.
In an embodiment of the present invention the metal phthalocyanine used is selected from cobalt and iron phthalocyanine.
In yet another embodiment of the present invention the halogenating agent used is selected from the group consisting of chlorine, bromine, iodine, thionyl chloride sulphuryl chloride, phosphorous pentachloride, phosphorous oxychloride, phosphorous pentabromide, phosphorous tribromide, thionyl bromide and phosphorous trichloride most preferably selected from thionyl chloride, phosphorous pentachloride and chlorine.
In yet another embodiment of the present invention the inert organic solvent used is selected from O-dichlorobenzene and nitrobenzene.
In yet another embodiment of the present invention the halogenated metal phthalocyanine catalyst prepared is selected form the group consisting of dichloro, dibromo, diiodo, mono chloro, monobromo and monoiodo derivatives of metal phthalocyanine preferably selected from dichloro and dibromo derivative of cobalt and iron phthalocyanine.
In still another embodiment of the present invention a novel catalyst prepared by the present invention is useful for the sweetening of sour petroleum distillates as herein described with reference to the examples.
The novelty of the present invention lies in the process for the preparation of a novel halogenated metal phthalocyanine catalyst suitable for the sweetening of wide range of sour petroleum distillates boiling above 140xc2x0 C., like kerosene, jet fuel, fuel oil, naphtha, FCC gasoline in a fixed bed treating system. These higher boiling distillates generally contain mercaptans which are more difficult to oxidise, like tertiary mercaptans and aromatic thiols. The catalyst therefore has been evaluated with the feeds doped with various types of mercaptans in different concentrations as given in the examples. Although the supported catalyst of this invention is particularly applicable to the heavier petroleum distillates, it can also be used for the treatment of lower boiling distillates such as natural straight run and the cracked gasolines.
The following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.
Preparation of the Catalyst